Aiming device for mortars



April 4, 1961 Filed July 16, 1958 J. R. JASSE AIMING DEVICE FOR MORTARS 3 Sheets-Sheet 1 April 4, 1961 J. R. JASSE AIMING DEVICE FOR MORTARS 3 Sheets-Sheet 2 Filed July 16, 1958 April 4, 1961 Filed July 16, 1958 J. R. JASSE AIMING DEVICE FOR MORTARS 3 Sheets-Sheet 3 2,977,858 AIMING DEVICE FOR MORTARS Joseph Raymond Jasse, Paris, France, assignor to Hutchkiss-Brandt, Paris, France, a body corporate of France Filed July 16, 1958, Ser. No; 749,011 Claims priority, application France July 18, 1957 '7 Claims. 01. 89-41) r The present invention relates to aiming devices for mor- 1 tars and like firearms intended to be as a rule fired in any direction in azimuth,

The aiming device of a mortar generally comprises a sighting apparatus fixed on a mount connected to the morta'r barrel by releasing means, a reference or aiming mark disposed at a certain distance from the mortar and suitable control means for the mount whereby the mortar'is aimed. i

In general, the mortar is put in an initial direction:

termed an observation or datum direction determined, for example, by means of two suitably spaced aiming-posts.

In order to aim the mortar, the deflection drum of the sighting apparatus is turned so that the plane containing the'axis of the aiming telescopic sight and the axis of rotation of the deflection drum is parallel with the axis of the mortar barrel, the horizontality control device of the mortar is actuated to bring the bubble of the transverse spirit level between reference marks and the biped mount is moved by pivoting the mortar barrel in the socket or seat of the base-plate on which the rear end of the barrel rests, until the center of the cros wires of the sight of the sighting apparatus is in alignment with the aiming-posts determining the observation direction.

If, in firing, the mortar is displaced out of the line of fire due to the displacement of the base due to the efiect of the reaction of firing the shot, it is always possible to recover the desired position of the barrel by acting on the elevation and horizontally controls so as to bring the hubbles of the spirit levels between the reference marks and thereafter acting on the traversing control so as to bring the center of the cross wires of the sight on one of the aforementioned aiming posts, without touching the sighting apparatus.

If it is required to etfect a fire switch through a given 7 angle, that is, to change the direction of fire, for example through a certain angle toward the right, the known procedure is adopted in pivoting the deflection drum through the same angle toward the left and thereafter pivoting the mortar barrel toward the right until the center of the crosswires of the sight is once more on the aiming-post.

But if this post is not at infinity, that'is, if the new line' of sight is not parallel with the previous line of sight, the angle through which the barrel turns is less than the desired angle. The difference is greater as the aiming-post is nearer the mortar, since it is only when this post is at infinity that the new line of sight is parallel with the previous line of sight and that the desired fire switch is obtained.

Now, in practice, it is sometimes necessary to fire from a defiladed position (cave, shell hole, etc.) which does not permit an aiming mark to be placed at a sufficient distance (about 50 meters) to suitably reduce the aiming error in azimuth because the aiming mark is not at infinity (parallax error). r

If the aiming mark can only be positioned at a lesser distance from the mortar, for example, at 1.5 meters from i device notably in the case of firing in any direction in azimuth. l

The present inventionavoids these disadvantages.

The object of the invention is to provide an improved aiming device for mortars and like fire arms which are adapted to be fired if not in all directions in azimuth, at

least in directions which make with one another very large angles, this device permitting putting the mortar inobservation by means of a referencedevice which is located 1 very near the mortar (for example less than 2 meters), which permits firing even when this mortaris in a very defiladed position.

Said device comprises in combination with a sighting apparatus provided with a telescopic sight: support means fixed to the mount of the mortar and forming a slideway along which said sightingapparatus is movable as desired,

said slideway being oriented in such manner as to permit reducing the distance in plantfrom the axis of the telescopic sight of said apparatus to the vertical pivot axis of the mortar in the course of fire switches in azimuth while regulating said distance between two given limits, and a reference device 'so adapted that by observing the latter through the telescopic sight of the sighting apparatus it is possible to determine instantaneously and without ambiguity that the axis of the telescopic sight is perpendicular to saidreference device.

' Said referencedevice could be constituted notably by a mirror having two flat faces disposed at 90 to one another, or a prism equivalent to this mirror; or a series of projections comprising flat edges located in the same plane and lateral faces perpendicular to said plane whereby the line of sight of the telescopic, sight is perpendicular to said plane only when said lateral faces are not visible in the telescopic sight.

Obviously, the reference device should have sufilcient length so that whenthe fire arm changes direction, the prolongation of the axis of the sight perpendicular to this device still encounters this device. Now, if the sighting apparatus were fixed directly to the mount in the usual manner, that is, at a point relatively distant from the vertical axis about which the fire arm barrel turns in the course of fire switches in azimuthwhich axis in the case of a mortar intersects 'ithe point at which the rear of the barrel is supported on the base-plate anchored in the ground -this reference device would have to have a rather great length and in any case a length greater than the diameter of the circle described by the telescopic sight when firing in alldirections in azimuth.

Owing to the fact that the sighting apparatus is carried by the aforementioned slide-way fixed on the mount, it is .possible to shift the sighting apparatus considerably toward the vertical axis about which the. barrel turns and in this way the lateral displacement of the line of sight of the telescopic sight is reduced, which correspondingly reduces the required length of the reference device. Thus,

owing to the aforementioned combination, the reference device has its transverse dimensions limited to some tens of centimeters. I

Briefly, the aiming device of the invention permits eliminating any parallax, since the successive lines of sight remain parallel with one another because they are Fig., l is an e'levational view of a mortar providedwith an aiming device embodying the invention;

Fig. 4 is a corresponding plan view thereof, partly in;

section, taken along line 4-4 of Fig. 3;

Fig. 5 is a vertical cross-sectionalview taken along line 5-5 of Fig. 3;

Fig. 6 is a. diagrammatic view ofthe forward end of.

the optical or telescopic sight of thesighting apparatus;

Figs. 7 and 8 are diagrammatic front views of the reference. device showing what is seen of this. device through the telescopic sight in daytime and at night respectively;

Fig. 9 is a diagrammatical vertical elevational View of the mirror having two. perpendicular faces forming part of the reference device showing the directions of the incident and reflected rays;

Fig. 10 is a diagrammatic plan view of two positions of the sight combined with a reference device comprising a series of plates which must be viewed solely by their forward edges of it is desired that the reference axis be, and remain, perpendicular to this reference device;

Figs. 11 and 12 show the appearance of this reference device through the telescopic sight when the reference axis is respectively perpendicular and oblique to the reference device, and

Fig. 13 is a diagram showing use of a fiat mirror.

In the embodiment shown in Figs. 1 and 2, the inven tion is applied to a mortar of conventional type comprising a mortar barrel A which rests at its rear end, through the medium of a ball in a spherical socket or seat a of a' baseplate B adapted to be anchored in the ground as soon as the first rounds have been fired and, at its forward end, on a rotatable mount C having three parts: a biped b, a clamping device for clamping the barrel A in position and a release device d interconnecting the biped b and the device 0 and adapted to withstand, at least up to a certain force, the recoils of the barrel; the biped is connected to the release device by a yoke e and a traversing screw The aiming device of the invention is combined with this mortar and comprises in combination: support means generally indicated by the reference character Dthis support means providing a slideway--a sighting apparatus E adjustable along said slideway and a reference device F. V

The support means D is shown on a small scale in Figs. 1 and 2 and on an enlarged scale in Figs. 3-5.

In this embodiment, the support'means is adapted to be fixed to the biped b of themount C and comprises four parts situated between the biped and the apparatus E: a first support member 1 adapted to be fixed to the mount; a straight arm 2 forming a slideway; an elastical- 1y yieldable connecting device 3 connecting the arm 2 to the support member 1; and a slide 4 movable along the arm 2 and adapted to receive the sighting apparatus E.

The support 1 comprises a base 5 to which is connected a tube 6 carrying at its end two members 7 and 8 which surround the tube 6. A male dovetail 11 (Fig. 4) is fixed to the ends of the members by a screw 9.and a. dowel 10 and is adapted to be engaged in afemale dovetail 11 (Fig. 2) formed in the yoke e of the biped."

The arm 2 constitutes a rectilinear slideway and has a prismatic cross-sectional shape, for example hexagonal, and is preferably tubular (Fig. 5 This arm is connected to the base 5 of the support 1 by the elastically yieldable device 3 which permits maintaining arm in a given orientation while allowing it to deviate,

following manner in the embodiment shown in Fig. 4.

Connected to the base 5 by a flange 12 and screws 13 is a housing 14 on which is thread an annular cover 15. Bearing against the transverse wall of the housing 14 through the medium of three balls 16 is the base 17 of a member 18 in which is formeda conical recess or seat 19. Fitted into this seat and held therein by a screw 20 is a conical male end 21of the arm 2. The base 17 of the member 18 is held elastically against the, balls 16. by springs 22 which are. concentric with the member 18 and bear against the base 17 and against a washer 23, which latter rests against-the inner annular face of thecover 15.

The base 17 is prevented from rotating relative tothe housing 14 due to the fact that the balls 16 are disposed in conical recesses 16 and16 provided in the members 17 and 14.

As mentioned hereinbefore, owing to the springs 22 the axis U-.-U of the arm 2 is maintained in a .fixed direction from which'it can be displaced elastically. This direction is chosen (see Figs. 1 and 2) in such manner that it is oblique relative to the longitudinal axis V--V of the barrel A in both the vertical and horizontal planes, the two axes U-U and VT-V forming between each other. an angule u in the vertical plane (Fig. 1). and an angle v in the horizontal plane (Fig. 2).

Preferably, the angle u is so chosen that the arm 2. is horizontal for a mean firing angle of this value of the angle u affording the most convenient position found in experience for the sighting apparatus E placed at the free end of the arm 2 (Figs. 1 and 2) irrespective of the angle of elevation.

The angle v in the horizontal plane is preferably about 10 to 20, which permits avoiding, as will be explained hereinafter, dead angles in respect of the sighting apparatus B when firing in any direction in azimuth.

The slide 4, which is movable along the arm 2, forms a clamp on this arm. It consists of a main portion 24 which has at its upper part 25 a female dovetail for receiving the sighting apparatus E, this portion also forming by two lugs 26 one of the jaws of theclamp, and by a depending portion 27 a support lever. Pivoted to the latter by means of the pin 28 is a second lever 29. consti-. tuting a second jaw 30. provided with clamping teeth 31. Aspring 32 disposed between the two levers 27 and 29 tends to swing the jaw 30 in a direction which applies the teeth 31 against the. arm 2 with sufiicient force for maintaining the clamping slide 4 and the sighting apparatus E in position. To move the unit (4-E). along the M1112 it is therefore sufiicient to take hold of the two levers 27 and 29 in one hand and to compress the spring 32-so as.

to separate the two jaws 30 and 26.

Thesighting apparatus E is of any conventional type permitting aiming in azimuth and elevation owing to, the provision of the screw 33 (elevation), the possibility of turning the deflection drum and the provision of the fine deflection adjustment screw 34 (Fig. 1), which permits shifting in. elevation-and azimuth the line of sight W.-W (Figs. 1 and 2) of a telescopic or optical sight 35 form ing part-of the sighting apparatus. This telescopic sight is capable of being looked into from above in the known manner, the eye-piece 36, being turned upwardly and its axis being disposed at to the line of sight W-W, thus providing the gun-layer with a comfortable position at the side of the fire, arm when aiming.

The-sight 35, is completed, accordingto the invention, by meanspermitting aneasy positioning of its, optical axis WW both during the day time and at night.

This sight, which. comprises the conventional cross wires. 3,7v (Fig, 6) further comprises at its forward end} a, ap 381. 5%. mid) which. s p o d t 39 d iaal; hen. aiminsas hawn n. igs 1 ndr hisfiaa;

amass comprises in its middle a wide black line 40 which stands outagainst a'white background41. I

Further, provided within the tube of the sight 35 to ward its forward end is a translucid screen 42 '(Fig. 6) whichis substantially in the form of a horse-shoe or a U and which, illuminated by an electric lamp 43 placed behind it, constitutes at night an easily located light source. This electric lamp 43 is fed with current by a batterywhich could be disposed either in the sight or in the clamp support 4.

The unit described hereinbefore iscompleted by the reference device F. This device comprises a tripod 44 7 (Figs. 1 and 2) provided with a spherical spirit level 45 permitting insuring that a support 46 is in a horizontal position. The support 46 carries a reflector system comprising two flat mirrors '47 and 48 disposed at 90 to one another so that any incident ray, such as the ray R or R (Fig. 9), is reflected in a direction parallel with itself, that is, in directions R; or R';; as known per se.

It will be observed that the support 46 for the mirrors is mounted relative to the tripod 44 for rotation about the axis XX which is vertical when the bubble 45' of the level is between its reference marks. The support 46 carries on its upper end a small arm 49 which can be moved to a position parallel with the mirrors but which in its extended position is normal to the joint line 50 of the two mirrors 47 and 48 (Figs. 7, 8 and 9).

The unit described hereinbefore operates in the following mannerz' The mortar having been placed in its observation direction SS (Fig. 2), the reference device F is preferably placed in-a position which is offset relative to the observation plane S--S at an angle s, and the mirror is oriented in such manner that the arm 49 is in line with the centre of the seat a and substantially with the axis of the sight 35 of'the sighting apparatus. The image of the end of the sight therefore appears in substantially the middle of the mirror which is the best position for firing in any direction in azimuth. Thedeflection corresponding to the angle s will be noted; it is the observation angle Before firing, it is necessary, as is known, to determine the'safe elevations, that'is, the minimum elevation corresponding to the highest obstacle over which'the line of fire must pass and maximum elevation corresponding to the'lowest obstacle under which the line'of fire must Pam To determine the safe of the sighting apparatus is adjusted in such manner as to render the plane of sight parallel with the plane of fire and the sighting apparatus is moved along the arm 2 to its extreme forward position where it is located, relative the barrel, substantially in the position it would occupy if it had been mounted directly on the yoke e of the biped b except for a slight difference in the lateral distance relative arrangement, provided between the sight and its support carried by the sighting apparatus. Then, by means of the elevation wheel of the mortar, the barrel and the sighting apparatus are moved simultaneously, so that the line of sight of the sight is flush with the topof the obstacle.

By acting on the elevation knob of the sighting apparatus, the elevation bubble is brought between the reference marks .andthe minimum (or maximum) elevation is read ofi the graduation of the elevation sector. 7

After having returned the sighting apparatus to its The teleto the line of intersection 50 of the two mirrors and, thereelevations, the deflection drum 6 initial position, in which it is pointed at the mirror, the unit is ready for firing in any direction in azmuth.

It will be understood that during firing, the mirror is left untouched; this mirror in fact replaces a reference point at infinity.

Let it be assumed that it is required to fire in the direction TT (Fig. 2) for which direction the axis V--V must be brought from the observation direction S-S, which corresponds to a fire switch to the right through an angle 2 (Fig. 2).

As the observation angle is equal to s to the left, the gun-layer effects the deflection (s-I-t) to the left and then orders a displacement of the barrel to the right, while he aims in the following conditions:

In the day time, he pivots the whole of the mortar about the vertical axis YY intersecting the center of the seat a and thus brings the center of the image 37 of cross wires 37 of the sight into coincidence with the middle of the black line 40 of the image 38 of the background 41 appearing in the double mirror 4748, as shown in Fig. 7.

At night, the gun-layer causes the center of the cross wires to be projected at 37 (Fig. 8) on the axis of the image 42 of the suitably illuminated translucid screen 42.

It will be easily understood that the coincidences 37 40 (Fig. 7) or 37, 42 (Fig. 8) are only possible so long as the reflected ray has the same direction in plan as the incident ray, which necessarily implies that this ray is perpendicular to the mirror.

Consequently, when coincidence is obtained, it is certain that the line of sight WW of the sight isirrespective of the position of the mortar and sightperpendicular fore, makes an angle .9 with the observation direction 8-8. The line of sight can only be more or less offset laterally therefrom depending on the amplitude of the fire switch, and this olfset in lateral translation is, as is known, quite negligible bearing in mind the dimensions of the target and the dispersion of the fire.

Thus the axis VV of the barrel is definitely directed in direction TT corresponding'to the direction of fire to be effected after the setting of the fire switch angle t and the following reference setting.

The fire switch thus obtained without the slightest error of parallax is a consequence of the utilization of the double mirror 47-48 which provides, owing to the coincidences of the images 40 or 42 (Figs. 7 and 8) and of the cross wires 37, the certainty that the lines of sight remain constantly parallel with the initial line of sight and in other words affords the equivalent of a reference mark at infinity.

This result would be obtained even if the sighting apparatus B were fixed directly in the dovetail 11 of the yoke e of the mount C (Fig. 2) but, in this case, owing to firing in any direction in azimuth, the pivot axis of the telescopic sight would describe a circle I (Fig. 2) having a center Y of very large diameter, exceeding a meter,

and for the positions E or E of the sighting apparatus,

situated at the two ends of the diameter parallel with the joint line of the two mirrors 47 and 48, aiming would be possible along the lines of sight E W and E -W only if the mirrors of the reference device F extended to these lines of sight, as shown in dot-dash line in Fig. 2.

As mentioned hereinbefore, this would lead to a prohibitive size of the reference device F. v

This is avoided owing to the support D forming part of the combination of the invention. It can be seen that as the sighting apparatus E is moved away from the elastically yieldable device 3 toward the free end of the arm 2, the circle described by the pivot axis of the tele scopic sight in the course of fire switches decreases progressively. Thus in the position of the sighting apparatus shown in Figs. 1 and 2, the circle-becomes that shown by the line II which has a very small radius; the

extreme lines of sight are then E W and which can 'fallwithin the set of mirrorsshown inthe drawings, the length of which can therefore be restricted to some tens tit centimeters.

The'double oblqu'ity ll, y given totheaxis U -U ofthe arm 2 provides (the additional advantage of eliminating any dead angle in the aiming, that is to say for all direc tions offire there is at least one position of the sighting ap paratus E along this annfor which the line of sight is not i intersected by the barrel, which occursfor a range of directions of fire when the telescopic sight occupies a fixed position on the mount.

Thus, in Fig. 2, assuming thatthc reference device is at H and the sight is disposed at 35 it is clear that the line of sight SS -"W would intersect the barrel A;

whereas the line. of sight il -W passes over thisbarrel tion toward the free end of the arm.

The. reference device F described hereinbefore has the advantage of permitting obtaining a correct aim irrespective of the elevation of fire or more precisely the in'clina-' tion relative. to the vertical of the optical axis of the sight, 35' at the moment of. aiming, since whatever the said su'pportelement so as to be obliquewith respect to ,the'longitudinal axis ofthe gun barrel both in vertical directionan'din horizontaldirectidn, slidemovablealong: said slideway,-and'--a sighting device with a line'of sight carried by saidsIide, so that the displacement of the lat ter along said slideway makesit possibleto reduce thedistance in plan from said line of sight tosaid vertical when the sighting. apparatus E is in. the, illustrated. posi-- I direction of the incident ray R or R the reflected ray R' or R remainsparallel with the incident ray and is received in the sight (Fig 9).

Fig. 10 shows a modification of the reference device 1 adapted to be turned toward the sight 35, as situated in the sameplane 22 which isparallel to slide F the line of sight W-W the sides 52 of these plates 50 which are perpendicular to slide F being then parallel with the line .of sight. Thus,'if .the suitable aimis obtained, that is, if the line W-'-W is perpendicular to Ethe' plane Z Z, the series of blades is viewed simply from the edges 51 as sliownin Fig. ll. If, on the other hand, the

sight is disposed at (Fig. 10) so that the line of sight is oblique to the plane ZZ and is incorrect, the gun-layer observes in the eye-piece of the sight 35* the blades 50 both from the edges 51 and their large sides 52 which indicates that the mortar must be turned a further distance about the axis YY to obtain that the view in the sight of tho deference device F be in conformity with that shown in Fig. 11.

Fig. 13 shows a modification of the reference device which comprises a single flat mirror 53 whose length corresponds to that of the two mirrors of the first example. However, in this modification which isperfectly suitable when the sight is disposed horizontally at 35 at the level of the median horizontal line of the mirror, it is essential Having now described my invention WhatI claim as new.

and desire to secure by Letters Patent is:

1. A firearm including at least one rotatable portion mounted rotatably about a vertical axis and a barrel connected with said rotatable portion and the longitudinal axis of which may be inclined relatively to said vertical axis; an aiming apparatus comprising in combination: a reference device spaced from said verticalaxis and of a relatively small length comparedwith the distancethereo-f from said. vertical axis to determine Whether a line of sight passing close to said vertical. axis. is perpendicular to said reference device, and anaiming device comprising a support element which is rigidly and laterally connected with said rotatable portion, a rectilinear slidew'ay fixed" on When. i the aim is correct; this plane must be perpendicular to axis of rotation of the rotatable portion of the firearm to a-value which is; at most, equalto :the leugth-ofthe 10 reference device. I I 2. 1m. combination: a firearrnincluding" at least one rotatable portionmouuted rotatably' about avertical-axis and a gun barrel the longitudinal axis-of which may be I inclined relatively to said vertical axis,and an aiming apparatusfor said firearm comprising: a refcrencedevice spaced from said vertical axis and-of arelatively small 1 size compared to the distance thereof from said vertical axis to permitdetermining whether a line-of sightpassingcloseto said vertical axis is perpendicular to said refer ence device, and an aiming device comprisinga support element rigidly andlaterallyt connected with the rotatable portion of the-firearm, a rectilinear slideway fixed on said.

support; element so as to be oblique relatively to the longi- 'tudinal axis of the gun barrelboth in vertical direction and in horizontal direction, a slide movable: along said :slideway, and a sighting device with a line of sight'carried by said slidein-such a manner that the; displacement of, I I the latter along said islideway makes it possible toreduce :the distance in plan from said line of sight to said of. the reference device.

'3." e ombination'according toclairn 2, wherein said I firearm is a mortarwhich comprises: base plate, said the slideway being fixed laterallyon saidmount.

4. A firearm including at least one rotatable portion mounted rotatably about a vertical axis and agun barrel connected" with saidportion and the longitudinal axis of which may be inclined relatively to said vertical axis! an aiming apparatus comprisinga' support element rigidly and laterally fixed on said rotatable portion of the fire arm, a rectilinear slideway fixed on said support-element so asto be oblique relatively to the longitudinal axis of the gun barrel both in vertical direction and inhorizontal direction, aslide movablewalongsaid slidway, and a sighting device with a line of sight carriedby said slide 5. A firearm including at least one rotatable portion mounted rotatably about a vertical: axis and a gun barrel connected with said portionand the longitudinal axisof which may be inclined *relatively to said vertical axis; an

aiming-apparatus comprising asupport element rigidly-andlaterally'fix'ed on said rotatable-portion of thefi'rearm, a rectilinear slideway, elastic means. for fixing said. slideway on said support element, so that said-slideway, when ina position of'rest established by the elastic means, is oblique with respect to the longitudinal axis of the: gun barrel both in vertical directionv and in horizontal direction, a slide movable along said slideway, anda sightingrdevicewitha line of sight carried by said slide in. such a manner that the displacementof the latter along. said slideway. makes it possible. to. reduce. the distance in. plan. from said line of. sightfto the vertical. axis of rotation of 'the. rotatable portion of the-firearm. I

6. An aiming device according to claim-5,]wherein said support element'fincludes a cup comprisingafibottom. and a flange spaced'from' saidbottom, said flange being devertical axis of rotation of therotatable porti'ontof-the, I I firearm to a-value which is, atmost, equal to the length i gun barrel being mounted pivotably on said plate about :1

- fixed pivoting center and a mount of adjustable height on I I which rests and is fixed on the gun barrelwhich forms ,withsaid mount' said portion of" the firearm which is rotata'ble about said vertical axis, said supportelement ,of I

tachable, said arm comprising a base parallel to said bottom, balls interposed between said bottom and said base,

and an elastic device interposed between said base and said flange to urge the base against said bottom through the medium of said balls.

7. A firearm including at least one rotatable portion mounted rotatably about a vertical axis and a gun barrel connected with said portion and the longitudinal axis of which may be inclined relatively to said vertical axis; an aiming apparatus comprising in combination: on the one hand, a reference device spaced from said vertical axis and which comprises a flat slide of a relatively small length compared to the distance between the vertical axis and said reference device and adapted to be horizontal in operative position, and a series of projections on said slide, said projections having extremities in a plane parallel to said slide and lateral faces perpendicular to said slide, and, on the other hand, an aiming device comprising a support element rigidly and laterally fixed on the rotatable portion of the firearm, a rectilinear slideway fixed on said support element so as to be oblique relatively to the longitudinal axis of the gun barrel both in vertical direction and in horizontal direction, a slide movable along said slideway, and a sighting device with a line of sight carried by said slide in such a manner that the displacement of the latter along said slideway makes it possible to reduce the distance in plan from said line of sight to the vertical axis of rotation of the rotatable portion of the firearm to a value which is, at most, equal to said length of the reference device, a correct aiming being realized when said line of sight is parallel to said lateral faces of the projections of the rule.

References Cited in the file of this patent UNITED STATES PATENTS 2,491,476 Brown Dec. 20,1949 2,660,794 Goertz et a1 Dec. 1, 1953 2,696,144 Herlach Dec. 7, 1954 2,732,766 Weiss et a1. Jan. 31, 1956 2,780,964 Jasse Feb. 12, 1957 

